Yvette Guilbert’s unwanted freckles
Follow the conservators as they remove stains and blemishes from a range of late-19th century lithographs.
A stained portrait
In 1894 the French cabaret singer and actress Yvette Guilbert was splendidly portrayed by the painter and graphic artist Henri de Toulouse-Lautrec in an album comprising 16 colour lithographs accompanied by texts. The National Gallery of Denmark owns an extensive collection of prints by Toulouse Lautrec, and this collection includes a unique and complete copy of this work. Six of the sheets and the album cover are currently featured in the exhibition Toulouse Lautrec – The Human Comedy.
As part of the preparations for the exhibition, the Yvette Guilbert album underwent extensive conservation treatment. Earlier water damage had left the work with dark discolorations in the form of more or less intense spots evenly distributed throughout the entire album. The damage was very obvious and disrupted the overall impression to an unacceptable degree.
First, each individual sheet was gently dry cleaned with a soot sponge to remove any dirt on the surface. Then the leaves were analysed individually under a microscope and the effect of cleaning by means of water and ethanol was tested. Unfortunately, these products seemed to have little impact on the discolorations; clearly, stronger means were called for.
Hydrogen peroxide is an oxidising disinfectant and bleach. Mild solutions of hydrogen peroxide are used for a variety of common household tasks, such as disinfecting skin inflammations and cleaning contact lenses or toothbrushes. In more concentrated solutions the product has a very strong bleaching effect on colours, and when we carried out a test on our original material we saw that hydrogen peroxide could clearly reduce the colour intensity of the spots.
One by one, each spot was bleached by means of a 10% hydrogen peroxide/water solution. The oxidising agent presents a health hazard, so the task was performed under ventilation and the product was applied with a fine, long-haired brush to ensure maximum precision and control. Once the cleaning agent had dried up slightly the process was repeated; these repetitions continued over and over until the spot had been reduced to a point where it was acceptable. To make the working process as efficient as possible, the process alternated between the front and back of the work. It was important to stop regularly to consider the effect of the bleaching; things can happen very quickly, and overbleaching (i.e. white spots) can be as disruptive to the overall impression as the original dark stains.
Consequences of the process
Bleaching by means of hydrogen peroxide not only affects the colour of the paper fibres; it also weakens them. So the conservator must monitor the condition of the paper throughout the entire bleaching process.
Oxidising agents are tough on paper. So when treating works on paper, bleaching should only be carried out in those cases where the stains or damage is more pronounced than the motif itself and where the paper is thick, strong and stable.
The final part
Finally, each sheet from the album was bathed in water to remove any chemicals left behind by the bleaching process and then dried. During the spot bleaching the addition of moisture inevitably causes small areas of the paper to rise and become slightly deformed; this was resolved by drying the paper under controlled conditions in order to make it level again.
Discover the artworks in the current exhibition about Henri de Toulouse-Lautrec from 9 September – 2 February 2012